\documentclass[11pt,a4paper]{article}
\usepackage{fontspec}
\setmainfont[BoldFont=SimHei,ItalicFont=KaiTi_GB2312]{SimSun}
\setsansfont[BoldFont=SimHei]{KaiTi_GB2312}
\setmonofont{Microsoft YaHei}

\begin{document}
世界,你好!
\end{document}
